1. Field of the Invention
The present invention relates to an automatic sample injecting apparatus (hereinafter referred to as an “automatic sampler”) for suctioning a sample from a sample container containing the sample so as to inject the suctioned sample to an analyzing device such as a liquid chromatograph.
2. Description of the Related Art
An automatic sampler is generally provided with a needle for suctioning and ejecting a sample, a mechanism for moving the needle, a metering pump, and a valve for switching connection between a plurality of passages (see, for example, Unexamined Patent Application Publication No. 2005-265805).
There are two systems for an automatic sampler: a total amount injection system and a loop injection system. In an automatic sampler of a total amount injection system, a sample loop is connected between a needle and a metering pump via a valve, to then be filled with a sample suctioned in a larger amount than the volume of the sample loop, followed by switching the valve in such a manner as to connect the sample loop onto a passage of an analyzing device, so that the sample is injected to the analyzing device by the amount equivalent to the volume of the sample loop. In other words, in the automatic sampler of the total amount injection system, the volume of the sample loop per se is basically equivalent to the amount of the sample to be injected to the analyzing device, and therefore, the reproducibility of the amount of sample to be injected to the analyzing device is excellent. However, with this system, the sample spilling from the sample loop is discharged to a drain, and therefore, the sample is largely consumed.
In contrast, in an automatic sampler of the loop injection system, a sample loop is positioned on a base end side of a needle. A predetermined amount of sample suctioned by a metering pump is made to stay in the sample loop, and then, the sample is injected to an analyzing device. That is to say, in the automatic sampler of the loop injection system, the amount of sample suctioned by the metering pump is equivalent to the amount of sample to be injected to the analyzing device. Therefore, a suction error made by the metering pump signifies an error of the injection amount as it is, thereby affecting the reproducibility of the amount of sample to be injected to the analyzing device.
In the case where deficient suction occurs in the metering pump or the amount of sample in the sample container is insufficient in the automatic sampler, the amount of sample to be injected to the analyzing device is smaller than the predetermined amount, thereby possibly affecting an analysis result. This problem is more conspicuous in the loop injection system. Only the amount of sample less than or equal to the volume of the sample loop can be possibly suctioned due to deficient suction by the metering pump also in the total amount injection system, thereby raising a problem.
In order to confirm whether or not the sample is normally suctioned from the sample container, an analyzer needs to take out a rack including the sample containers before and after an analysis, measure the weight of the sample container by using a scale, and determine a decrease in weight of the sample contained inside of the sample container. In the case where the determined amount of suctioned sample is different from a predetermined value, a calibration coefficient is determined by using the determined amount of suctioned sample and the predetermined amount of suctioned sample. The resultant calibration coefficient needed to be multiplied by a signal strength obtained by the analysis for the purpose of correction. Here, the calibration coefficient is a coefficient obtained by dividing a predetermined suction amount by an actual suction amount. For example, in the case where the actual suction amount is only 90% of the predetermined suction amount, the calibration coefficient becomes 1.11 obtained by dividing 1 by 0.9.
As described above, in order to verify whether or not the sample is normally suctioned from the sample container, the analyzer needed to measure the decrease in amount of sample contained inside of the sample container after the analysis so as to confirm the decrease. However, this verification requires the manual work of the analyzer, thereby raising the problems of an increase in time and labor, and further, occurrence of artificial errors.
There has been known an analyzing device in which a weight sensor is disposed in a scale having a solution bottle mounted thereon, a sensor signal cable is connected to an input terminal, and then, a sensor signal is input into the input terminal when the weight of the solution bottle becomes a predetermined value or lower, thus stopping a system or issuing an alarm, so as to prevent an idle operation of the system (see Unexamined Patent Application Publication No. 8-145975).